1. Field of the Invention
The present invention generally relates to mobile communication systems.
In a general way, mobile communication systems are subject to standardisation; therefore a detailed description of such systems can be found in the corresponding standards, published by the corresponding standardisation bodies, such as for example 3GPP (3rd Generation Partnership Project).
2. Description of the Prior Art
It is simply recalled that the architecture of mobile communication networks is logically divided into an Access Network (AN) and a Core Network (CN), and the architecture of the Core Network is logically divided into different domains, including a Circuit Switched (CS) domain and a Packet Switched (PS) domain.
An example of such systems is the GSM/GPRS system, wherein, as recalled in FIG. 1:                the AN, called Base Station Subsystem (BSS), comprises network elements such as in particular Base Transceiver Station (BTS) and Base Station Controller (BSC),        the CN comprises network elements such as in particular Mobile Switching Center (MSC) for the CS domain, and Serving GPRS Support Node (SGSN) for the PS domain.        
It is recalled that the radio access technology used by GSM is based on Time Division Multiple Access (TDMA), where the transmission structure on the radio interface between AN and Mobile Station (MS) is organised in frames in turn organised in timeslots.
As recalled in FIG. 3, resource management procedures in systems such as GSM include the sending by the MSC to the BSS of an Assignment Request message according to the BSS Management Application Part (BSSMAP) protocol, and the sending by the BSS to the MS of an Assignment Command message according to the Radio Resource Control (RRC) protocol.
As specified in 3GPP TS 44.018, the Assignment Command message contains a description of the channel configuration to be used by the MS. In particular, the Assignment Command message contains a Channel Mode Information Element, which gives information on the mode of coding/decoding and transcoding, and is coded as follows:
Bits8765432100000000signalling only00000001speech full rate or half rateversion 100100001speech full rate or half rateversion 201000001speech full rate or half rateversion 310000001speech full rate or half rateversion 410000010speech full rate or half rateversion 510000011speech full rate or half rateversion 601100001data, 43.5 kbit/s (downlink) +14.5 kbps (uplink)01100010data, 29.0 kbit/s (downlink) +14.5 kbps (uplink)01100100data, 43.5 kbit/s (downlink) +29.0 kbps (uplink)01100111data, 14.5 kbit/s (downlink) +43.5 kbps (uplink)01100101data, 14.5 kbit/s (downlink) +29.0 kbps (uplink)01100110data, 29.0 kbit/s (downlink) +43.5 kbps (uplink)00100111data, 43.5 kbit/s radio interface rate01100011data, 32.0 kbit/s radio interface rate01000011data, 29.0 kbit/s radio interface rate00001111data, 14.5 kbit/s radio interface rate00000011data, 12.0 kbit/s radio interface rate00001011data, 6.0 kbit/s radio interface rate00010011data, 3.6 kbit/s radio interface rate
Thus, in GSM specifications, the bitrate over the radio interface for one timeslot is defined in the Channel Mode Information Element. With Enhanced Data rates for GSM Evolution (EDGE) technology, it is possible to go up to a maximum bit rate of 43.5 kbit/s with a single timeslot.
In a general way, in order to enable such systems (such as for example the above recalled GSM system) initially mainly designed to support telephony services, to support higher bit rate services (such as in particular videotelephony services), a multislot allocation mechanism has been specified, enabling to allocate several timeslots to a Mobile Station, instead of a single timeslot.
Thus, in GSM specifications, it is possible for the MSC to request high bit rates via the Assignment Request message over the A interface. In particular, this allows the support of 64 kbit/s H.324M video-telephony and higher bit rates.
To support the multislot allocation mechanism, the Assignment Command message contains a “Description of the multislot configuration (Multislot Allocation)” Information Element followed by a list of “Mode of Channel Set” Information Elements. The purpose of the Multislot Allocation Information Element is to provide a description of which channels are used in downlink and uplink respectively, in a multislot configuration. It also groups the channels into Channel Sets, used to identify channels that carry related user information flows which therefore need to be handled together. The Channel Mode for each Channel Set can be defined by a separate “Mode of Channel Set” Information Element.
In other words, in GSM specifications, a combination of several timeslots, allowing higher bitrates, is possible and defined in the Assignment Command message via the “Description of the multislot configuration” Information Element.
In a general way, there is also an evolution of such systems towards fixed-mobile convergence.
An example of such an evolution corresponds to a system wherein mobile services can be provided by the same Core Network to a Mobile Station not only via an Access Network such as for example the above recalled Base Station Subsystem of GSM, but also via an Access Network using a fixed (Broadband) network.
An example of an Access Network using a fixed network corresponds to the Unlicensed Mobile Access Network (UMAN) or the Generic Access Network (GAN), as specified in particular in UMA specifications and in 3GPP specifications, providing a complement to the traditional coverage provided by systems such as GSM/GPRS.
As recalled in FIG. 2, the architecture for UMAN/GAN comprises, in particular, the following elements:                Mobile Stations (MS),        Unlicensed Network Controller (UNC)/Generic Access Network Controller (GANC).        
The UNC/GANC appears to the CN as a BSS. The UNC/GANC communicates with the CS domain via the A interface, and with the PS domain via the Gb interface. The MS and the UNC/GANC communicate via a Broadband or Generic IP Access Network (not specifically illustrated in FIG. 2) supporting high bit rates. The interface between UNC/GANC and MS is called Up interface. UMAN/GAN uses wireless technologies such as for example Bluetooth or WiFi, enabling to support high bit rates.
More generally, such Access Network supporting high bit rates (such as UMAN/GAN network) will also be called hereinafter broadband Access Network, as opposed to a non broadband Access Network (such as for example the BSS or Radio Access Network of GSM).
As recalled in FIG. 4, resource management procedures in a system such as the one illustrated in FIG. 2 include the sending by the MSC to the UNC/GANC of an Assignment Request message according to the BSS Management Application Part (BSSMAP) protocol, and the sending by the UNC/GANC to the MS of an Activate Channel URR/GA-CSR message, as specified in UMA/3GPP specifications.
The Activate Channel URR/GA-CSR message contains UMA/GAN bearer path setup Information Elements, such as in particular Channel Mode, UDP Port & IP Address for the uplink RTP stream, . . . etc. The Channel Mode Information Element gives information on the mode of coding/decoding and transcoding.
According to the current state of UMA/3GPP specifications, the Channel Mode Information Element as defined in 3GPP TS 44.018 has been reused in the Activate Channel URR/GA-CSR message.